1. Field of the Invention
The present invention relates to a work attracting apparatus and a work attracting method used in the process of manufacturing semiconductor devices and the like.
2. Description of the Related Art
In the process of manufacturing semiconductor devices and the like, trays stream consecutively like in a belt-conveyor. Wafers are mounted on the trays. In each process, wafers are received from trays streaming consecutively. A processing assigned to each process is performed on the wafers, and the wafers are returned onto trays and sent out to another of the processes. A work attracting apparatus performs receiving and sending out wafers in each process. In particular, it is required that wafers be received and sent out in a non-contact manner in the process of manufacturing semiconductor devices and the like. Hence, performing such operation precisely and in a short time is one of the most difficult manufacturing technologies.
For example, for a conventional work attracting apparatus used for a normal-pressure CVD apparatus and the like in the semiconductor manufacturing process, wafers processed in the previous processes stream thereto consecutively. When a wafer arrives at a predetermined position, a Bernoulli chuck following the Bernoulli principle moves down to the wafer, attracts the wafer, and takes into its own process. The permissible time from when a wafer arrives at a predetermined position to when a Bernoulli chuck moves down to and attracts the wafer was about 4 seconds.
The Bernoulli chuck following the Bernoulli principle refers to a arm-shaped chuck that ejects gas (usually nitrogen gas) through a nozzle in the center of the attraction plate to have high speed gas flow along the surface of a wafer and thereby generates negative pressure to hold the wafer on the attraction plate in a non-contact manner. An example of the technology for using the Bernoulli chuck in the semiconductor manufacturing process is disclosed in, for example, Japanese Patent Laid-Open Publication No. 51-37573 (pp. 1–3, FIG. 1).
Furthermore, a technology is disclosed in, for example, Japanese Patent Laid-Open Publication No. 9-237818 (Abstract), with which a wafer transfer apparatus (equivalent to the work attracting apparatus of the present invention) mounts a work onto the receiving portion with restricting an impulse given to the work to as little as possible so that the work transfer apparatus operates precisely, while keeping a transport mechanism transporting works at high speed.
In the above prior art, the permissible time from when a wafer arrives at a predetermined position to when a Bernoulli chuck moves down to the wafer and attracts the wafer is as short as about 4 seconds, and hence it is difficult to perform precise attraction operation by the Bernoulli chuck.
Meanwhile, it is hard to adopt lengthening the permissible time for attraction because it would lower the efficiency in manufacturing semiconductor products. Moreover, in the process of manufacturing semiconductor devices and the like, where it is required that wafers be received and sent out in a non-contact manner, it is hard to adopt chucks other than the Bernoulli chuck in terms of performing attraction operation certainly.